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<title>13.10.1 Database Objects </title>
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<h2><a name="SECTION00151010000000000000000"></a><a name="dbhash-objects"></a>
<br>
13.10.1 Database Objects 
</h2>

<p>
The database objects returned by <tt class="function">open()</tt> provide the methods 
common to all the DBM-style databases and mapping objects.  The following
methods are available in addition to the standard methods.

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2528' xml:id='l2h-2528' class="method">first</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  It's possible to loop over every key/value pair in the database using
  this method   and the <tt class="method">next()</tt> method.  The traversal is ordered by
  the databases internal hash values, and won't be sorted by the key
  values.  This method returns the starting key.
</dl>

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2529' xml:id='l2h-2529' class="method">last</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Return the last key/value pair in a database traversal.  This may be used to
  begin a reverse-order traversal; see <tt class="method">previous()</tt>.
</dl>

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2530' xml:id='l2h-2530' class="method">next</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Returns the key next key/value pair in a database traversal.  The
  following code prints every key in the database <code>db</code>, without
  having to create a list in memory that contains them all:

<p>
<div class="verbatim"><pre>
print db.first()
for i in xrange(1, len(db)):
    print db.next()
</pre></div>
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  <td><nobr><b><tt id='l2h-2531' xml:id='l2h-2531' class="method">previous</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  Returns the previous key/value pair in a forward-traversal of the database.
  In conjunction with <tt class="method">last()</tt>, this may be used to implement
  a reverse-order traversal.
</dl>

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  <td><nobr><b><tt id='l2h-2532' xml:id='l2h-2532' class="method">sync</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
  This method forces any unwritten data to be written to the disk.
</dl>

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